Magnetic properties and magnetocaloric effect in RE_(55)Co_(30)Al_(10)Si_(5)(RE=Er and Tm)amorphous ribbons

The magnetic and magnetocaloric effects(MCE)of the amorphous RE_(55)Co_(30)Al_(10)Si_(5)(RE=Er and Tm)ribbons were systematically investigated in this paper.Compounds with R=Er and Tm undergo a second-order magnetic phase transition from ferromagnetic(FM)to paramagnetic(PM)around Curie temperature T_(C)~9.3 K and 3 K,respectively.For Er_(55)Co_(30)Al_(10)Si_(5) compound,an obvious magnetic hysteresis and thermal hysteresis were observed at low field below 6 K,possibly due to spin-glass behavior.Under the field change of 0 T–5 T,the maximum values of magnetic entropy change(-△S_(M)^(max))reach as high as 15.6 J/kg·K and 15.7 J/kg·K for Er_(55)Co_(30)Al_(10)Si_(5) and Tm_(55)Co_(30)Al_(10)Si_(5) compounds,corresponding refrigerant capacity(RC)values are estimated as 303 J/kg and 189 J/kg,respectively.The large MCE makes amorphous RE_(55)Co_(30)Al_(10)Si_(5)(RE=Er and Tm)alloys become very attractive magnetic refrigeration materials in the low-temperature region.

Giant low-field cryogenic magnetocaloric effect in polycrystalline LiErF4 compound

Antiferromagnetic LiErF4has attracted extensive attention due to its dipolar interaction domination and quantum fluctuations action. In the present work, the crystal structure, cryogenic magnetic properties, and magnetocaloric effect(MCE) of polycrystalline LiErF4compound are investigated. Crystallographic study shows that the compound crystallizes in the tetragonal scheelite structure with I41/a space group. It exhibits an antiferromagnetic(AFM) phase transition around 0.4 K, accompanied by a giant cryogenic MCE. At 1.3 K, the maximum values of magnetic entropy changes are 24.3 J/kg·K,33.1 J/kg·K, and 49.0 J/kg·K under the low magnetic field change of 0–0.6 T, 0–1 T, and 0–2 T, respectively. The giant MCE observed above Néel temperature TNis probably due to the strong quantum fluctuations, which cause a large ratio of the unreleased magnetic entropy existing above the phase transition temperature. The outstanding low-field MCE below 2 K makes the LiErF4compound an attractive candidate for the magnetic refrigeration at the ultra-low temperature.

Magnetic properties and magnetocaloric effects of Tm_(1-x)Er_(x)CuAl(x=0.25,0.5,and 0.75)compounds

We investigate the structural,magnetic,and magnetocaloric effects(MCE)of Tm_(1-x)Er_(x)CuAl(x=0.25,0.5,and 0.75)compounds.The compounds undergo a second-order phase transition originating from the ferromagnetic to paramagnetic transition around 3.2 K,5 K,and 6 K,respectively.The maximum magnetic entropy changes(-△S_(M)^(max))of Tm_(1-x)Er_(x)CuAl(x=0.25,0.5,and 0.75)are 17.1 J·kg^(-1)·K^(-1),18.1 J·kg^(-1)·K^(-1),and 17.5 J·kg^(-1)·K^(-1)under the magnetic field in the range of 0-2 T,with the corresponding refrigerant capacity(RC)values of 131 J·kg^(-1),136 J·kg^(-1),and 126 J·kg^(-1),respectively.The increase of-△S_(M)^(max)for Tm0.5Er0.5CuAl may be relevant to the change of magnetic moment distribution of Er and stress coming from element substitution.This work provides several compounds that can enrich the family of giant MCE materials in the cryogenic region.

Giant low-field reversible magnetocaloric effect at liquid helium temperature of niobium and iron co-substituted EuTiO_(3) compounds

Giant magnetocaloric effect(MCE)materials in the liquid helium temperature region have attracted a lot of attention in the field of low-temperature magnetic refrigeration(MR).In this study,a series of niobium(Nb)and iron(Fe)co-substituted EuTiO_(3) perovskites with cubic structure(space group pm3m)was successfully fabricated,and their magnetic properties as well as cryogenic magnetocaloric effects were investigated in detail.As expected,the introduction of Nb and Fe can significantly modulate the magnetic phase transition and magnetocaloric effect of the EuTiO_(3) compounds.With increasing Fe concentration,two local minima corresponding to the AFM-FM magnetic phase transition near 5.0 K and FM-PM transition near 10 K with no hysteresis in the thermomagnetic curves are observed,which is attributed to an enhancement of FM coupling.At the same time,the gradually widened-ΔSM-T curves and the two peaks with a broad shoulder lead to considerable refrigeration capacity(RC).With the field change ofΔH=2 T,the calculated values of-ΔS_(M)^(max) for the EuTi_(0.9375-x)Nb_(0.0625)Fe_(x)O_(3)(x=0.075,0.1,0.125,0.15)compounds are 24.2,17.6,14.5 and 14.0 J/(kg·K),respectively.The corresponding RC values were calculated to be 144.6,138.3,151.2 and 159 J/kg,respectively.Especially,the values of-ΔS_(M)^(max) for EuTi_(0.8625)Nb_(0.0625)Fe_(0.075)O_(3) are 8.6 and 15.1 J/(kg·K)under low field changes of 0.5 and 1 T,respectively.The giant low-field reversible magnetocaloric effect makes them attractive candidates for magnetic refrigeration in the liquid helium temperature region.

Magnetic properties and magnetocaloric effects in Eu(Ti,Nb,Mn)O_(3) perovskites

In perovskite EuTiO_(3),the magnetic characteristics and magnetocaloric effect(MCE) can be flexibly regulated by converting the magnetism from antiferromagnetic to ferromagnetic.In the present work,a series of Eu(Ti,Nb,Mn)O_(3) compounds,abbreviated as ETNMO for convenience of description,was fabricated and their crystallography,magnetism together with cryogenic magnetocaloric effects were systematically investigated.The crystallographic results demonstrate the cubic perovskite structure for all the compounds,with the space group of Pm3m.Two magnetic phase transitions are observed in these second-order phase transition(SOPT) materials.The joint substitution of elements Mn and Nb can considerably manipulate the magnetic phase transition process and magnetocaloric performance of the ETNMO compounds.As the Mn content increases,gradually widened-ΔS_(M)-T curves are obtained,and two peaks with a broad shoulder are observed in the-ΔS_(M)-T curves for Δμ_(0)H≤0-1 T.Under a field change of 0-5 T,the values of maximum magnetic entropy change(-ΔS_(M)^(max)) and refrigeration capacity(RC) are evaluated to be 34.7 J/(kg·K) and 364.9 J/kg for EuTi_(0.8625)Nb_(0.0625)Mn_(0.075)O_(3), 27.8 J/(kg·K) and367.6 J/kg for EuTi_(0.8375)Nb_(0.0625)Mn_(0.1)O_(3),23.2 J/(kg·K) and 369.2 J/kg for EuTi_(0.8125)Nb_(0.0625)Mn_(0.125)O_(3),17.1 J/(kg·K) and 357.6 J/kg for EuTi_(0.7875)Nb_(0.0625)Mn_(0.15)O_(3),respectively.The co nsiderable MCE parameters make the ETNMO compounds potential candidates for cryogenic magnetic refrigeration.

Large low-field reversible magnetocaloric effect in K_(3)Gd(PO_(4))_(2) at sub-Kelvin temperature

We synthesized a potassium gadolinium phosphate K3Gd(PO_(4))_(2)with monoclinic structure(P2_(1/m))by the high-temperature solid-state reaction method.Its lattice constants obtained by Rietveld refinements of XRD curve are a=0.7411 nm,b=0.5624 nm,and c=0.9433 nm.Magnetic and magnetocaloric properties of K_(3)Gd(PO_(4))_(2)were investigated in detail.The magnetic phase transition temperature of K3Gd(PO_(4))2 was determined by ultra-low temperature testing to be 0.58 K.K_(3)Gd(PO_(4))2 exhibits large magnetic entropy changes(-ΔSM).The maximum-ΔSM are 20.2 and 29.4 J/(kg·K)in the magnetic field variation(ΔH)of 1 and 2 T,respectively,which are larger than that of the commercial Gd_(3)Ga_(5)O_(12)(GGG).The maximum adiabatic temperature change(ΔT_(ad))reaches 5.91 K under a magnetic field change(ΔH)of 1 T.K_(3)Gd(PO_(4))_(2)is a potential magnetic refrigeration material for obtaining sub-Kelvin temperatures.

Large reversible magnetocaloric effect in antiferromagnetic Er_(3)Si_(2)C_(2) compound

The magnetic properties,magnetic phase transition and magnetocaloric effects(MCE) of Er_(3)Si_(2)C_(2) compound were investigated based on theoretical calculations and experimental analysis.Based on the first principles calculations,the antiferromagnetic(AFM) ground state type in Er_(3)Si_(2)C_(2) compound was predicted and its electronic structure was investigated.The experimental results show that Ei_(3)Si_(2)C_(2) compound is an AFM compound with the Neel temperature(T_(N) of 7 K and undergoes a field-induced firstorder magnetic phase transition from AFM to ferromagnetic(FM) under magnetic fields exceeding 0.6 T at 2 K.The magnetic transition process of Er_(3)Si_(2)C_(2) compound was investigated and discussed.The values of the maximum magnetic entropy change(-ΔS_(M)^(max)) and the refrigeration capacity(RC) are 17 J/(kg·K)and 193 J/kg under changing magnetic fields of 0-5 T,respectively.As a potential cryogenic magnetic refrigerant,the Er_(3)Si_(2)C_(2) compound also provides an interesting research medium to study the magnetic phase transition process.

Fabrication and growth mechanism of one-dimensional Heusler alloy nanostructures with different morphologies on anodic aluminum oxide template by magnetron sputtering

Heusler alloys are a kind of intermetallic compounds with highly-ordered arrangement of atoms.Many attractive functional materials have been developed in Heusler alloys.Due to the application requirements of materials in new-generation electronic devices and spintronics devices,one-dimensional nanostructured Heusler alloys with special functions are needed.In this work,it is proposed to grow one-dimensional Heusler alloy nanostructures(1D-HA-NSs)by magnetron sputtering plus anodic aluminum oxide(AAO)template.Nanowires with different shapes,amorphous-coated(AC)nanowires and nanotubes were successfully grown for several Heusler alloys.AC nanowires are the unique products of our method.Heusler alloy nanotubes are reported for the first time.The one-dimensional nanostructures grow on the surface of the AAO substrate rather than in the holes.The top of the pore wall is the nanostructure growth point,the shape of which determines the morphology of the nanostructures.A general growth mechanism model of one-dimensional nanostructures on AAO template was established and further confirmed by experimental observation.

Large reversible cryogenic magnetocaloric effect in rare earth iron carbides of composition RE_(2)FeC_(4)(RE=Ho,Er,and Tm)

At cryogenic temperatures,the investigations of magnetic phase transition and magnetocaloric effect in RE_(2)FeC_(4)(RE=Ho,Er,and Tm) compounds were performed.Ho_(2)FeC_(4)and Er_(2)FeC_(4)compounds undergo two magnetic phase transitions with the temperature decreasing:from paramagnetic(PM) to ferromagnetic(FM) transition at their respective Curie temperature(Tc) and from FM to antiferromagnetic(AFM) or ferrimagnetic(FIM) transition below 2 K.Tm_(2)FeC_(4)compound exhibits only a second-order PM to FM phase transition at TC=K.Large reversible MCE without hysteresis loss is observed in RE_(2)FeC_(4)(RE=Ho,Er,and Tm) compounds.Particularly,the maximum value of magnetic entropy change(-ASM)is 21.62 J/(kg K) under the magnetic field change(Δ_(μ0)H) of 0-5 T for Er_(2)FeC_(4).The Er_(2)FeC_(4)compound presenting excellent magnetocaloric performance makes it a competitive cryogenic magnetic refrigeration material.

TmNi_(2)Si_(2)化合物中不稳定的反铁磁性和大的可逆磁热效应

基于实验和理论结果,我们对TmNi_(2)Si_(2)化合物的磁性,磁相变和磁热效应进行了研究.TmNi_(2)Si_(2)化合物被证实存在不稳定的反铁磁相互作用,并在超过0.2 T的外加磁场下发生从反铁磁到铁磁的场驱动变磁转变.此外,大的可逆低温磁热效应也被观察到.在0-2 T的变化磁场下,最大磁熵变和制冷量分别为15.4 J kg^(-1)K^(-1)和68.0 J kg^(-1).因此,低磁场下大的可逆磁热效应表明TmNi_(2)Si_(2)化合物在低温磁制冷机中具有潜在的应用前景.

Enhanced low-field magnetocaloric effect in Dy-doped hexagonal GdBO_(3) compounds

Borates have attained increasing attention attributed to their excellent thermal stability,distinctive thermodynamic property,and high mechanical strength in recent years.A series of polycrystalline Dydoped GdBO_(3) compounds was prepared,their crystal structures,magnetic properties,and cryogenic magnetocaloric effects were comprehensively investigated.The compounds crystallize in hexagonal structure(space group P6_(3)/mmc),the lattice constant decreases with the increase of Dy content.Dydoping in GdBO_(3) significantly reduces critical magnetic field and enhances low-field magnetocaloric effect.The maximum magnetic entropy changes for the Gd_(1-x)Dy_(x)BO_(3)(x=0.6,0.8,and 1)compounds in a field change of 2 T surpass 17.3 J/(kg·K)at 2.5 K,enhanced by nearly 120%compared to GdBO_(3)(8.0 J/(kg·K)).Besides,the corresponding refrigeration capacity increases from 33.9 to 62.2,57.2,and 72.5 J/kg,respectively,with an enhancement of 70%-110%.The considerable maximum magnetic entropy change,refrigerating capacity,and temperature averaged entropy change make them competitive candidates for cryogenic magnetic refrigeration.

Exploration of the rare-earth cobalt nickel-based magnetocaloric materials for hydrogen liquefaction

Magnetic refrigeration based on the magnetocaloric effect(MCE)of magnetic solids has been considered as an emerging technology for hydrogen liquefaction.However,the lack of high-performance materials has slowed the development of any practical applications.Here,we present a family of rare-earth cobalt nickel-based magnetocaloric materials,namely Dy_(1-x)Ho_(x)CoNi and Ho_(1-x)Er_(x)CoNi compounds,and system-atically investigated their structural and magnetic properties as well as the MCE and magnetocaloric per-formance.All of these compounds crystallize in the C15-type Laves-phase structure and undergo typi-cal second-order magnetic phase transition(MPT).The change in magnetism and the MPT temperature for the Dy_(1-x)Ho_(x)CoNi and Ho_(1-x)Er_(x)CoNi compounds originate from the exchange interactions between nearest-neighbor RE 3+ion pairs.No hysteresis magnetocaloric effect was achieved,and the MPT tem-perature of these compounds could be tuned from the liquefaction temperature of nitrogen(∼77 K)to hydrogen(∼20 K)by adjusting the ratio of rare-earth elements.This study’s findings indicate that theDy_(1-x)Ho_(x)CoNi and Ho_(1-x)Er_(x)CoNi compounds are of potential for practical magnetic refrigeration applica-tions in the field of hydrogen liquefaction.

Efficacy,safety and immunogenicity of hexavalent rotavirus vaccine in Chinese infants

A randomized,double-blind,placebo-controlled multicenter trial was conducted in healthy Chinese infants to assess the efficacy and safety of a hexavalent live human-bovine reassortant rotavirus vaccine(HRV)against rotavirus gastroenteritis(RVGE).A total of 6400 participants aged 6-12 weeks were enrolled and randomly assigned to either HRV(n?3200)or placebo(n?3200)group.All the subjects received three oral doses of vaccine four weeks apart.The vaccine efficacy(VE)against RVGE caused by rotavirus serotypes contained in HRV was evaluated from 14 days after three doses of administration up until the end of the second rotavirus season.VE against severe RVGE,VE against RVGE hospitalization caused by serotypes contained in HRV,and VE against RVGE,severe RVGE,and RVGE hospitalization caused by natural infection of any serotype of rotavirus were also investigated.All adverse events(AEs)were collected for 30 days after each dose.Serious AEs(SAEs)and intussusception cases were collected during the entire study.Our data showed that VE against RVGE caused by serotypes contained in HRV was 69.21%(95%CI:53.31-79.69).VE against severe RVGE and RVGE hospitalization caused by serotypes contained in HRV were 91.36%(95%CI:78.45-96.53)and 89.21%(95%CI:64.51-96.72)respectively.VE against RVGE,severe RVGE,and RVGE hospitalization caused by natural infection of any serotype of rotavirus were 62.88%(95%CI:49.11-72.92),85.51%(95%CI:72.74-92.30)and 83.68%(95%CI:61.34-93.11).Incidences of AEs from the first dose to one month post the third dose in HRV and placebo groups were comparable.There was no significant difference in incidences of SAEs in HRV and placebo groups.This study shows that this hexavalent reassortant rotavirus vaccine is an effective,well-tolerated,and safe vaccine for Chinese infants.

Enhanced low-field magnetocaloric effect in Nb and Al co-substituted EuTiO_(3)compounds

The magnetic ground state switching between antiferromagnetic(AFM)and ferromagnetic(FM)states in EuTiO_(3)provides the feasibility of regulating its magnetic properties and magnetocaloric effect.First-principles calculations demonstrate that the magnetic ground states for EuTi_(0.875)Nb_(0.0625)Al_(0.0625)O_(3),EuTi_(0.8125)Nb_(0.125)Al_(0.)0_(625)O_(3),and EuTi_(0.75)Nb_(0.125)Al_(0.125)O_(3)are FM coupling.Experimental results also exhibit the FM coupling domination in these compounds,accompanied by a significantly enhanced low magnetic field magnetocaloric effect.The maximum magnetic entropy change of all the samples surpasses15 J kg^(-1)K^(-1)with a field change of 1 T.which is 1.4 times as large as that of bulk EuTiO_(3).Especially,the maximum refrigerating capacity for EuTi_(0.8125)Nb_(0.125)Al_(0.0625)O_(3)compound is evaluated to be 88.1 J kg^(-1),more than three times of that of EuTiO_(3).The remarkable magnetocaloric performances prove Nb and Al co-substituted EuTiO_(3)compounds to be competitive candidates for magnetic refrigeration in the liquid helium temperature regime.

Effects of 1,9-dibromnonane on the structural, photophysical properties and stability of cesium lead bromide perovskite nanocrystals

The CsPbBr3@Cs4PbBr6 nanocrystals(NCs) could be synthesized by multiple Cs-oleate injections as adding the 1,9-dibromnonane in the reaction solution. The 1,9-dibromnonane could provide Br-ions and the rich Br-ions effectively restrain the generation of Cs Br. The Cs4 PbBr6 wrapped around the Cs Pb Br3 NCs and the size of crystalline grain was increased with increasing the Cs-oleate as excess oleylamine. The quantum yield for 14 S4 DN reached to 99.3% due to the decrease of defects and the surface passivation of Cs4 PbBr6. There are more oleylammonium bromide on the surface of Cs Pb Br3 NCs as synthesized with1,9-dibromnonane. The ligand shell and the surface passivation of Cs4 PbBr6 restrained the decomposition of surface, consequently improved the stability of moisture and light for Cs Pb Br3 NCs. When the CsPbBr3@Cs4PbBr6 NCs were immersed in water under UV light(365 nm) for 2 h, the PL intensity could retain 90.4%, while the 11 S1(traditional Cs Pb Br3 NCs) was only 10.9%. It indicated the stability of moisture and light for Cs Pb Br3 NCs were greatly improved, because Cs4 PbBr6 NCs effectively passivated the surface of Cs Pb Br3 NCs and restrained the generation of traps states.